Screw conveyer



Dec. 1, 1942. w. M. SCHWEICKART 2,303,534

SCREW GONVEYER Filed May 16, 1940 2 Sheets-Sheet l BY W, 6 0. r fiATTORNEYS 1, 1942- w. M. SCHWEICKART ,30 ,5

SCREW CONVEYER v Filed May 16, 1940 2 Sheets-Sheet 2 INVENT R W 5 vWATTORNEYS Patented Dec. 1, 1942 w UNITED STATES PATENT OFFICE sonnwCONVEYER William M. Schweickart, Euclid, Ohio, assignor to PocohontasFuel Company Incorporated, New York, N. Y., a corporation of VirginiaApplication May 16, 1940, Serial No. 335,564

' 1 Claim. (01. 198 -213) This invention relates to the feeding of finegranulated material such as coal slack andparticularly to the feeding ofsuch material by a screw conveyer within a tube.

The object of the invention is to provide a screw feed which will beeflicient in action and avoid any jamming of the conveyer flight withinthe feed tube due to the accumulation and packing ofmaterial between thetube and the screw, particularly when the material is wet.

In the accompanying drawings illustrating apparatus adapted to practicethe invention,

Fig. 1 is a diagrammatic view of. a stoker installation embodying theinvention;

Fig. 2 is an enlarged longitudinal section of a portion of the coalconveyer thereof along its axis, taken as indicated by the line 22 ofFig. 3;

Fig. 3 is a vertical sectional view taken along the lined-3 of Fig. 2;

Fig. 4 is an enlarged view of a portion of the conveyer of Fig. 2, asindicated therein, with portions shown diagrammaticallyjto assist thedescription of the invention;

Figs. 5A, 5B and. 5C are diagrammatic sketches to assist the descriptionof the invention;

Figs. 6 and 7 show the blade of the conveyer screw in certain of itsstages of manufacture;

Fig. 8 is an enlarged vertical section of a modified form of coalconveyer; and

Fig. 9 is a vertical sectional view taken alon the line 9--9 of Fig. 8.

Referring to Fig. 1, the furnace I is equipped with an automatic coalburner or stoker ll having a driving motor and other equipment within ahousing l2. The stoker is of the bin feed type, that is, the stokerautomaticaly conveys the coal from the bin l3 into the furnace II),where the stoker feeds the coal to a suitable burner, not shown. Thecoal conveyer of the stoker includes the coal feed tube M and a worm orcoal screw l positioned within the coal tube Referring now to Figs. 2and 3, the coal feed tube I4 is a smooth cylindrical inner surface orbore which is substantially co-axial with the coal screw IS. The coalscrew l5 has a core or shaft portion [6 and screw flights orconvolutions ll spirally arranged along the core. Thus, when the screwis rotated, as by the stoker motor, the screw advances the coal alongthe tube 14 from the bin l3 into the furnace I0.

When the coal conveyer as so far described conveys fine coal, such asbituminous slack, which is wet, vthere is a tendency, as the screwrotates, for coal to accumulate and pack on the interior surface of thecoal tube and to build up to such height as to impede the rotation ofthe screw and overload the motor. Under the action of the screw themoisture tends to cement the fine particles of coal together into a hardcoating upon the interior of the coal tube, thus decreasing theeffective diameter of the tube so that the hard coating in time engagesthe edge of the screw and very substantially increases the torquerequired to rotate the screw. Such building up of a hard layer of coalsometimes progresses to the point of seizing the screw and stopping thefeed altogether. This tendency for coal to pack and form a hard layerupon the inside of the tube is more pronounced, and thepossibility ofmotor overload and screw seizure more likely, with increasing amounts ofmoisture contained in the coal. It has been found that fine bituminouscoal with a moisture content of about 7% and over has a very markedtendency to pack.

According to this invention the wet coal tending to form into a layer orcoating upon the inner surface of the tube is subjected to a groovingaction generally transverse to the direction of travel of the coal andthe grooved surface is then exposed to the pressure and wearing actionof the coal as it moves along the tube. This grooving action tends todisturb and break up any formative layer of coal which may tend to buildup, and th subsequent action of the traveling coal upon the disturbedand weakened layer further tends to disperse and remove it. The groovingaction takes place along the coal tube with the spaces betweensuccessive grooves sufficiently small to insure adequate dispersion ofthe intervening material between the grooves. Any accumulated layer ofcoal on the inner sur face of the tube is thus broken down at itsinception so that objectionable packing is prevented and overloads andscrew seizures overcome.

The grooving is effected by a series of projections I9 provided alongthe edge iii of the screw blade H, the projections extending outwardlyin continuation of the screw blade. The projections are of substantialheight, such as D, in comparison to the clearance (C plus D) between theinside surface of the coal tube I4 and the edge I8 of the coal screw atthe base of the projections IS. The projections have substantially thesame width as the thickness E, of the screw blade I1, and are ofrelatively small length, F, in comparison to the spacing G, betweensuccessive projections, both measured along the edge of the screw blade,so that the axial distance, H, between the paths described by successiveprojections is small in comparison to the axial length, I, of theprojections I9.

For clarity, only the top level of the coal is shown in Figs. 2 and 3,this level being indicated by the dot-and-dash lines LC, the level LCshown in Fig. 2 being the average level, or that directly above the axisof the screw. The dotted line R indicates the loci of the edge of thecoal screw l8 at the base of projections l9, and the diagrammatic andindicative of the action which is taking place.

In Figs. 4 and 5B the main current of coal? is indicated at 23 and theouterbody of coal, here the portion adjacent the bottom of the coal tubeI4, is indicated at 20. When-the coal is wet, there is a tendency forthe outer body of coal 2!] to pack and form a hard layer or coatingwhich gradually encroaches upon the coal screw.

A projection I9 is shown scoring into and grooving the outer body ofcoal 20. This action not only tends to form a groove or valley 2! in thecoal between-crests 22, but also to disturb and agitate the coal in thevicinity of the groove and crests and to produce cracks therein, thusweakening this body of coal.

When the rotation of the screw carries projection I9 beyond the areaunder consideration (as shown in Fig. 50) the groove 2| is first filledby an inrush of coal from the main current of coal 23, this inrushtending to disintegrate the already weakened groove formation. Then thecoal in the groove, being subjected to at least some of themotion-producing pressure to which the main current of coal 23 issubjected, bears against the far crest 22 of the groove and thispressure further tends to disintegrate the same. The movement of themain current of coal 23 relative to the outer body of coal 2!] alsotends to disintegrate the latter. Finally, as the projection l9 againapproaches the area under consideration, the coal in the groove inadvance of the projection is subjected to pressure and also displaced,and this pressure upon, and motion of, the coal in the groove likewisetends to disintegrate the groove formation.

As between successive grooves, the axial distance H therebetween issuch-that the crest 22 between the grooves is relatively weak, thisweakness being aided by the cracks produced at opposite sides and basesof the crest, some of which cracks tend to meet. Furthermore, the widthH of the crest is such in comparison to the axial spacing I betweencrests and the height D of the crest is such in relation to the width ofand spacing between crests, that the main current of coal 23 is able toobtain a relatively effective purchase upon the crest 22 and therebyaccelerate its disintegration.

As a result, any tendency for the outer body of coal 20 to pack andbuild up into a layer or coating is opposed by the layer-disintegratingprocess caused by the interaction of the projections l9 and the movementof the coal. Furthermore, as the formative layer advances in itsformation to a harder and harder consistency, the cracks therein causedby the projection l9 become longer and more numerous with the resultthat the nearer the outer body of coal 20 becomes to a hard layer themore rapidly it is disintegrated. In this manner the layer of coal onthe coal tube is thus destroyed while it is forming, so that the layerof coal is prevented from forming, or at least is maintained at such alow height as to be unobjectionable.

In addition, the projections l9 tend to reduce the friction between thescrew and the outer body of coal 20, for only the projections, and notthe entire edge of the screw blade engage the por-- tion of such bodytending to form into a layer.

The projections l9 in the apparatus of Figs. 2 and 3 are substantiallyrectangular flat-topped lobes on the edge of the screw blade andintegral therewith. These projections are formed along the edge of flatribbon stock by the use of suitable rolling operations, the stock beforesuch rolling being as shown in Fig. 6 and the stock after such rollingbeing as shown in Fig. 7. The ribbon stock is then wound around theshaft Hi to form a helix thereon and then secured thereto as by welding,to form the complete coal screw l5.

Figs. 8 and 9 show a modified apparatus in whichthe projections l9. arespots or drops of metal applied to or deposited upon the edge of thescrew blade by welding. The projections 19 in this modification aresubstantially disc shaped with a dome-like tip surface.

As examples of conveyers embodying this invention the following detailsof conveyers according to Figs. 2 and 3 and Figs. 8 and 9 are given:

Figs. 2, 3

B Radius of coal. screw to tips of projections l inches 1-% inches CClearance between inside surface of coal tube and tips of theprojections {5; inch ,4, inch D Height of projections :51, inch 3 inch EThicknss of screw blade inch inch F Length of projections,

along edge of screw 4 inch to 4 inch G Space between successiveprojections, along edge of screw 1 inch 1% inch (av.) 11 Axial distancebetween the paths described by successive projections inch (is inch IAxial length of projections. inch to 4 inch J Pitch of screw blade 2%inches 2-,} inches K Radius of screw shaft inch inch The foregoingconveyers have been especially eifective in preventing jamming of coalscrews handling bituminous coal on the order of oneeight and one-quarterinch slack.

While the screw conveyer has been shown and described in connection witha bin feed type of stoker, it is equally applicable to other coal feeds.

I claim:

A conveyer adapted to convey fine particles of moisture-laden bituminouscoal comprising a substantially horizontal coal tube having asubstantially cylindrical inner surface, a coal screw positioned withinthe coal tube and having a predetermined loose clearance between theouter edge' of the helical screw blade and the inner surface of the coaltube, a series of small radial projections on the periphery of the coalscrew blade of a height substantially less than said clearance andhaving a peripheral coverage which is a relatively small proportion ofthe total periphery of the edge of the screw blade and spaced apart sothat as the coal is conveyed horizontally by said blade said projectionswill cut into any layer developing within said clearance space and forma series of grooves in said layer with separating ridges having greaterradial height than axial width and protruding into the path of theconveyed coalso as to break up the coating and disperse the accumulatinglayer and remove it without substantial increase in the torque on thecoal screw.

WILLIAM M. SCI-IWEICKART.

i I IMM CERTIFICATE OF CORRECTION. i Patent No 2, 505 ,58h. I E December'1, l9h2'.

- WILLIAM H. SCHWEICKART. I

It is hereby certified that error appears, in the above numbered patentrequiringporrection as follows: In the grant, lines 2 and 15, and in theheadingto the printed. specification, line h, name of assignee, for"Pocohontas" read "Pocahontasand that the said Letters Patent should beread with this correction therein that the s ame may conform to therecord of the casev inthe Patent Office.

Signed and sealed this 12th day of January, A. D. 19%.

I I Henry Vah Arsdale, (Seal) A-cting Commissioner of Patents}

